6. A game played by two or more persons, with twenty-eight pieces of wood, bone, or ivory, of a flat, oblong shape, plain at the back, but on the face divided by a line in the middle, and either left blank or variously dotted after the manner of dice. The game is played by matching the spots or the blank of an unmatched half of a domino already played
7. One of the pieces with which the game of dominoes is played. Fall like dominoes. To fall sequentially, as when one object in a line, by falling against the next object, causes it in turn to fall, and that second object causes a third to fall, etc.; the process can be repeated an indefinite number of times. Derived from an entertainment using dominoes arranged in a row, each standing on edge and therefore easily knocked over; when the first is made to fall against the next, it starts a sequence which ends when all have fallen. For amusement, people have arranged such sequences involving thousands of dominoes, arrayed in fanciful patterns. Domino theory. A political theory current in the 1960's, according to which the conversion of one country in south asia to communism will start a sequential process causing all Asian countries to convert to communism. The apparent assumption was that an Asian country with a western orientation was as politically unstable as a domino standing on edge. Used by some as a justification for American involvement in the Vietnam war, 1964-1972.